The present invention relates to a filter apparatus for improving filtration accuracy and preventing porous filter elements from being clogged with foreign matter, dirt and grime.
In general, some kinds of filter apparatuses are widely used in processes for manufacturing sugar, beer and the like. As one of them, there has been used a type of filter apparatus which has a plurality of filter cylinders supported, at their upper ends, by a support plate in a filter tank. Each filter cylinder has a plurality of filter elements connected to each other in series.
In the above conventional filter apparatus, liquid to be filtered is fed into the tank under pressure from an inlet of the tank, and the liquid is filtered by the filter cylinders. Then its filtrate is discharged from an outlet of the tank. Before the liquid to be filtered is processed through the filter cylinders of the filter, in general, liquid such as water for dissolving diatomaceous earth is passed through the filter cylinders for a specific period of time, so that a desirable thickness of the diatomaceous earth is drifted around the filter elements of each of the filter cylinders. Thereafter, the liquid to be filtered is passed through the filter cylinders so as to be filtered by the diatomaceous earth around the filter elements.
However, at the upper end of each filter cylinder, there may exist a region where the diatomaceous earth is not drifted properly around the filter cylinder. That is, the surface of a liquid to be filtered does not necessarily reach the upper end of each filter cylinder and an upper region of each filter cylinder immediately below the support plate for supporting each filter cylinder is often exposed to air because the surface of the liquid to be filtered is raised and lowered due to the change of feeding pressure of a pump.
At a region of each cylinder, which contacts the surface of the liquid, a pre-coated diatomaceous earth layer is apt to be broken by a rippling phenomenon. Accordingly, if the surface of the liquid to be filtered is moved vertically, the pre-coated diatomaceous earth layer around the region of the cylinder, corresponding to a distance through which the liquid surface is moved vertically, is broken.
If the level of the liquid to be filtered is raised after once the level of the liquid is lowered, the liquid to be filtered passes through the region of the filter cylinder where the pre-coated diatomaceous earth is broken. Accordingly, as the liquid passes through the filter cylinder without being filtered, the filtration efficiency of each filter cylinder decreases. Furthermore, the upper part of each porous filter cylinder may be clogged with fine particles of foreign matter, dirt, grime and the like.